JP3316881B2 - Method for producing catalyst for producing methacrylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a heteropolyacid catalyst used for producing methacrylic acid by gas phase catalytic oxidation. More specifically, the present invention relates to a method for producing a heteropolyacid catalyst used for producing methacrylic acid by subjecting methacrolein, isobutane, or the like to gas phase catalytic oxidation with molecular oxygen.

[0002]

2. Description of the Related Art Various catalysts for producing methacrylic acid by subjecting methacrolein to gas-phase catalytic oxidation have been proposed (JP-A-50-101316, JP-A-50-1425).
No. 10, JP-A-59-4445, etc.), and some of them have already been used for industrial-scale production. Further, catalysts for producing methacrylic acid by oxidative dehydrogenation of isobutyric acid (JP-A-57-72936, etc.) and oxidation of isobutyraldehyde (JP-A-57-144238, etc.) are well known.

Further, a catalyst for producing methacrylic acid and methacrolein by oxidizing isobutylene or tertiary butanol (JP-A-55-127328), and recently methacrylic acid and methacrolein are obtained by directly oxidizing isobutane. Catalysts (JP-A-2-42032, JP-A-3-6
No. 3139) has also been proposed.

[0004] Catalysts used in these reactions include:
It has a structure of a heteropolyacid containing molybdenum and phosphorus as a main component and / or a salt thereof.It is known that partial replacement of molybdenum with vanadium and addition of a cocatalyst component such as copper, antimony, and arsenic are effective. I have.

As to the preparation method, addition of carboxylic acid and the like (JP-A-51-136615), addition of pyridines (JP-A-57-177347), addition of quinolines (JP-A-60-209258) A method of using various additives such as addition of ammonium nitrate (Japanese Patent Application Laid-Open No. 57-165040) and aging the slurry at a temperature of 80 ° C. or higher using a raw material containing no nitrate group (Japanese Patent Application Laid-Open No. 59-12758).
No.) and baking in an inert gas atmosphere (Japanese Unexamined Patent Publication No. 57-165)
No. 040), and a sintering method such as sintering in an atmosphere of ammonia and water vapor (JP-A-58-61833).

[0006]

However, the problems with these known catalyst systems are that both the reaction yield (activity and selectivity) and the catalyst life in the oxidation of methacrolein, which have already been put to practical use, are low. Is not always sufficient to satisfy the following. For example, as compared with Mo-V-based composite oxide catalysts for producing acrylic acid from acrolein, not only reaction selectivity is poor but also reaction activity and life are poor,
Therefore, a large amount of catalyst is required, and the burden of equipment cost and catalyst cost is large at present. One of the main reasons why the catalyst has not been sufficiently developed is that it has not been industrialized even when using isobutane, isobutyric acid or the like as a raw material.
It is an object of the present invention to improve the existing catalyst to provide a catalyst having higher reaction activity, selectivity and long catalyst life.

[0007]

Means for Solving the Problems In order to achieve the above object, the present inventors have made intensive studies on the improvement of heteropolyacid catalysts. As a result, a catalyst prepared by a specific method achieves the above object. That is, the present invention has been achieved.

That is, the present invention provides a compound represented by the general formula: PaMobVcAsdXeYfOg (wherein P, Mo, V, As, and O represent phosphorus, molybdenum, vanadium, arsenic, and oxygen, respectively, and X is a group consisting of potassium, rubidium, cesium, and thallium. Y represents at least one element selected from the group consisting of copper, silver, bismuth, iron, cobalt, antimony, lanthanum and cerium, and subscripts a, b, c, d, e, f and g represent the atomic ratio of each element, and when b = 12, a, c and e are 0
Value of 3 or less not including (zero), d and f are 0 (zero)
And g is a value determined by the valence and atomic ratio of other elements), and is a methacrylic acid comprising a partially neutralized salt of a heteropolyacid substantially free of ammonium and sulfate groups. When producing a production catalyst, the pH of a solution obtained by dissolving or suspending all the catalyst raw materials in water has a pH of 3 to
9. A catalyst for producing methacrylic acid, characterized in that a solid obtained by concentrating and drying the solution is calcined at 400 to 500 ° C. in an inert gas atmosphere in the presence of an ammonium group and a sulfate group so as to fall within the range of 9. It is a manufacturing method of.

The basic structure of the catalyst of the present invention is a conventionally well-known partially neutralized salt of phosphomolybdic acid with potassium, rubidium, cesium and thallium.
Further, it contains vanadium as an essential component. Arsenic is effective in improving methacrylic acid selectivity, and it is recommended to add it for this purpose. Further, it is desirable that the Y element is also included because it has an effect on improving the reaction activity and selectivity.
In particular, when copper is selected, the effect is large.

[0010] Combinations of these elements are already known, but the performance of the catalyst largely depends on the preparation method such as raw materials, additives, and calcination methods together with its composition, and the specific preparation conditions of the present invention must be adopted. This results in a more efficient catalyst.

One requirement of the present invention is that the aqueous solution from which the catalyst precursor is prepared contains ammonium and sulfate groups at the stage of suspension. This can be easily achieved by using a raw material containing ammonium and a sulfate group.

It is preferable to use ammonium molybdate as a raw material for molybdenum and ammonium. When molybdenum oxide, phosphomolybdic acid or the like is used, it is necessary to add ammonia or the like so that the ammonium root falls within a predetermined range. As the vanadium raw material, ammonium metavanadate, vanadium pentoxide and the like can be used. Phosphorus and arsenic generally use phosphoric acid and arsenic acid, but may be used in the form of a salt with other essential components such as ammonium phosphate, ammonium arsenate or copper phosphate. The sulfate is conveniently introduced in the form of a sulfate of the X component such as potassium and / or the Y component such as copper. Of course sulfuric acid,
Ammonium sulfate or the like can be added. If a sulfate group is present in any of the raw materials, nitrates, chlorides, carbonates, hydroxides, phosphates and the like can be used as the other X component and Y component.

A liquid obtained by dissolving or suspending these raw materials in water is usually a suspension. The solution must have a pH in the range of about 3 to 9, and the solid obtained by evaporating the solution to dryness is a so-called Dawson-type heteropolyacid having a P: Mo ratio of 1: 9. Salt is the main component. If ammonium salt is not used, or if the pH of the solution is lower than 3 due to too much sulfate, the salt becomes a so-called Keggin structure salt having a P: Mo ratio of 1:12 from the stage of evaporation to dryness. A highly active catalyst as in the present invention cannot be obtained. When the pH is higher than 9, such as when the amount of ammonium root is relatively large, it is difficult to form a precursor polyacid, and the activity is also lowered. The amount of ammonium and sulfate is 6 moles per 12 moles of molybdenum.
１８18 mol, preferably 0.1-3 mol.

[0014] It is not clear why the use of sulfates gives a higher performance catalyst than the commonly used nitrates, etc., but the tendency of the crystal particle size in suspension to be smaller is observed. ing.

It is considered that this is advantageous for forming pores when components such as ammonium sulfate are volatilized in the firing step described below. Further, when molding, when adding an organic molding aid such as methoxycellulose or polyvinyl alcohol, there is a possibility that large heat generation will occur during firing when ammonium nitrate coexists, but in the case of ammonium sulfate coexistence does not have such a problem. It is advantageous.

The solution is heated at a temperature of about 80 ° C. to 250 ° C. for 1 hour.
Hours or more, more preferably about 11 hours using a closed pressurized container.
It is preferable to perform the heat treatment at a temperature of 0 ° C to 200 ° C.
When the heat treatment is not performed or the heating temperature is about 80 ° C. or lower, the catalyst has a low conversion to methacrylic acid. Also 2
Even if the temperature is higher than 50 ° C., the effect corresponding to the above cannot be obtained.
Although the processing time is not particularly limited, it is generally 1 to 24 hours. At this stage, some solid-liquid reaction proceeds, and the activity of the finally obtained catalyst becomes higher.

The suspension may be filtered to separate solids, but is usually concentrated and dried at a temperature of about 100 to 150 ° C.
The resulting solid contains ammonium and sulfate groups, some of which form salts of Dawson-type heteropolyacids. Further, although the existence state of the sulfate group is unknown, it is presumed that at least a part thereof forms ammonium sulfate. Since the solid after drying has little activity as it is, it must be fired and activated. In the calcination stage, the crystal transition from the Dawson type to the Keggin type occurs at about 200 to 300 ° C., and components such as free ammonium sulfate are removed by 370 ° C., but the activity alone is still low. In order to avoid adverse effects on the catalytic activity and strength due to rapid calcination, it is preferred that the calcination be performed in advance at a temperature of about 350 to 370 ° C. before calcination and activation in an inert gas atmosphere.

The activation is performed in an inert gas atmosphere at about 400 to
500 ° C., preferably about 420-450 ° C. for about 1 hour
The firing is performed for 10 to 10 hours. When calcined in air as usual, the decomposition and sintering of the heteropolyacid occur at 400 ° C. or higher and the activity decreases, and at 400 ° C. or lower, a large amount of ammonium and sulfate groups remain. After all activity is low. By baking at a temperature of 400 ° C. or more in an inert gas, substantially all of the ammonium radicals and sulfate radicals can be removed without destroying the structure of the heteropolyacid. After firing in an inert gas atmosphere, firing may be performed at about 400 ° C. or lower in air.

JP-A-54-144311 and JP-A-5-143
No. 7-11895 discloses a catalyst using a sulfate as a raw material for preparing a catalyst and containing a sulfate group or a sulfur component as a catalyst component. Are clearly different.

Since the product fired in an inert gas is in a slightly reduced state, it may be further fired in air at a temperature of about 400 ° C. or less, reoxidized, and used for the reaction.

The catalyst of the present invention is used in various reactions such as oxidation of methacrolein. When used, the catalyst is used alone or in the form of being supported or diluted and mixed on a carrier such as alumina, silica or silicon carbide. In the case of a floor, it is used after being shaped into a column, a sphere, a ring, or the like.
It can also be used in the form of a reaction such as a fluidized bed or a moving bed.

When methacrylic acid is produced by catalytically oxidizing methacrolein in the gas phase using the catalyst obtained in the present invention, the raw material to be used is not necessarily required to be pure methacrolein, but may be isobutylene or tertiary acid. A methacrolein-containing gas obtained by the gas phase catalytic oxidation of lybutanol, or a gas obtained by vaporizing methacrolein obtained by a liquid phase method may be used. The oxygen source can be pure oxygen,
Air is used industrially.

As other diluent gases, nitrogen, carbon dioxide, carbon monoxide, water vapor and the like can be used. The concentration of methacrolein in the reaction raw material gas is about 1 to 10%, and the ratio of oxygen to methacrolein is about 1 to 5 or so. The space velocity of the raw material gas is preferably in the range of about 500 to 5000 h ^-1 , and the reaction temperature is preferably about 260 to 340 ° C.
The reaction pressure is usually carried out near normal pressure or under a slight pressure.

When isobutane is directly oxidized using the catalyst obtained in the present invention to produce methacrylic acid or methacrolein, the isobutane concentration in the raw material gas is about 15%.
% Is better. Pure oxygen,
Oxygen-enriched air, air or the like is used. A suitable ratio of oxygen to isobutane is about 0.2-2.

It is desirable that the reaction gas contains steam in a range of about 3 to 30%. Nitrogen in the source gas,
Carbon dioxide, carbon monoxide and the like may be contained as a diluent gas. Since the conversion cannot be so high in this reaction, unreacted isobutane and possibly oxygen are recovered and recycled.

The by-product methchlorene is recycled or led to another reactor and oxidized to methacrylic acid. Space velocity is about 30
The reaction temperature is preferably from about 270 to 340 ° C. at 0 to 3000 h ⁻¹ . The reaction pressure is usually performed at normal pressure or under pressure.

The catalyst obtained in the present invention can also be used for the production of methacrylic acid by oxidative dehydrogenation of isobutyric acid and oxidation of isobutyraldehyde. It can also be used when producing methacrylic acid from isobutylene in one step. In these reactions, the same reaction conditions as in the oxidation of methacrolein can be employed.

[0028]

The catalyst of the present invention has high reaction activity, selectivity and long catalyst life in the production of methacrylic acid.

[0029]

EXAMPLES The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples. The definitions of the conversion and the selectivity are as follows. Conversion (%) = [(moles of carbon atoms of reacted raw material) ×
100] ÷ (moles of carbon atoms in the supplied raw material) Selectivity (%) = [(moles of carbon atoms in generated product)
× 100] ÷ (number of moles of carbon atoms in the reacted raw material)

Example 1 Ammonium molybdate was added to 330 ml of ion-exchanged water.
((NH_Four)₆Mo₇O _{twenty four}・ 4H_TwoO) 296.5 g
And ammonium metavanadate (NH_FourVO_Three8.1)
9% dissolved in 85% phosphoric acid (H_ThreePO_Four) 2
4.2 g, 60% arsenic acid aqueous solution (H_ThreeAsO_Four13.3)
g, 50% cesium sulfate aqueous solution (Cs_TwoSO _Four) 70.
3g and copper sulfate (CuSO_Four・ 5H_TwoO) 10.5 g
Add and dissolve 225 ml of ion-exchanged water, mix
Was. In the obtained slurry, ammonia was contained per 12 moles of Mo.
It contains 10.8 mol of ammonium root and 1 mol of sulfate group.
H was about 6.0.

The slurry was concentrated using a rotary evaporator and dried at 120 ° C. in an electric furnace. The dried product at this stage has a 2θ (CuKα) of 9.6 °, 1
1.1 ゜, 12.4 ゜, 15.5 ゜, 19.1 ゜, 2
It has peaks at 0.7 °, 22.7 °, 25.9 °, 27.6 °, etc., and has a so-called Dawson-type heteropolyacid salt structure.

This is crushed, water is added and the diameter is 5 m with a mold.
m, extruded to a length of about 7 mm, and then
It was baked at 20 ° C. for 5 hours. This was analyzed by X-ray diffraction.
5 ゜, 18.4 ゜, 23.8 ゜, 26.1 ゜, 30.2
It had a peak at ゜, etc., and was a so-called Keggin-type heteropolyacid salt.

Further, this was fired in a nitrogen stream at 450 ° C. for 5 hours, and fired in air at 390 ° C. for 3 hours. As a result of X-ray diffraction, the catalyst had a Keggin-type heteropolyacid salt structure. In addition, the results of analysis of ammonium radical and sulfate radical were all below the detection limit (0.01% by weight). The composition of this catalyst was P _1.5 Mo ₁₂ V _0.5 As _0.4 Cs _1.4 Cu
_0.3 (excluding oxygen and hydrogen).

9 ml of this catalyst was filled in a glass reaction tube having an inner diameter of 15 mm, and a raw material gas having a composition consisting of 4 mol% of methacrolein, 12 mol% of oxygen, 16 mol% of steam and the balance of nitrogen was supplied at a space velocity (based on STP). ) At 670 h ^-1 , an activity test was conducted at a reaction temperature of 280 ° C. through a reaction tube. As a result, the conversion of methacrolein was 84.5%, and the selectivity of methacrylic acid was 87.0%.

Comparative Example 1 Cesium nitrate (CsNO) was used instead of the cesium sulfate aqueous solution.
₃ ) 38.2 g and copper nitrate (CuNO) instead of copper sulfate
₃ · 3H ₂ O) except for using 10.2g A catalyst was prepared in the same composition in the same manner as in Example 1. The X-ray diffraction of this catalyst was the same as in Example 1. In an activity test similar to that in Example 1, the conversion of methacrolein was 70.3% and the selectivity of methacrylic acid was 88.2%. It can be seen that the activity is low when nitrate is used instead of sulfate.

Example 2 296.5 g of ammonium paramolybdate was dissolved in 330 ml of ion-exchanged water, and 85% phosphoric acid 2
4.2 g, 60% arsenic acid aqueous solution 13.3 g, copper sulfate 10.
A solution prepared by dissolving 5 g of a 50% cesium sulfate aqueous solution (70.3 g) in ion-exchanged water (225 ml) was mixed, precipitated and precipitated, further added with vanadium pentoxide (6.38 g), and the slurry was transferred to a 1-liter autoclave. The heating and stirring process was performed for a time. In this slurry, 10.3 mol of ammonium group and 1 mol of sulfate group per 12 mol of molybdenum.
PH was about 5.8. The slurry was dried at 120 ° C. for 5 hours. Thereafter, a catalyst having the same composition as in Example 1 was prepared in the same manner as in Example 1. As a result of the activity test similar to that in Example 1, the conversion of methacrolein was 9
3.4% and methacrylic acid selectivity was 83.9%.

Comparative Example 2 85% phosphoric acid was used as 21.0 g, and instead of copper sulfate, phosphoric acid was used.
Copper (Cu_Three(PO_Four) _Two・ 3H_TwoO) 6.05 g, sulfuric acid
Cesium carbonate (Cs) instead of cesium_TwoCO _Three) 3
Example 1 was repeated in the same manner as in Example 2 except that 1.3 g was used.
A catalyst having the same composition was prepared. Activity test similar to Example 1
The result of conversion of methacrolein was 78.3%,
The selectivity of the phosphoric acid was 86.4%. Active compared to Example 2
It turns out that the property is low.

Example 3 A solution prepared by dissolving 296.5 g of ammonium paramolybdate in 330 ml of ion-exchanged water was added with 85% phosphoric acid 2
4.2 g, 3.5 g of copper sulfate, 90.4 g of a 50% aqueous cesium sulfate solution and 7.0 g of 98% sulfuric acid (H ₂ SO ₄ ) dissolved in 225 ml of ion-exchanged water were mixed, and vanadium pentoxide was further added. 8 g was added, the slurry was transferred to a 1 liter autoclave, and heated and stirred at 120 ° C. for 5 hours. The slurry contains molybdenum 12
10.3 mol of ammonium root and 1 mol of sulfate per mol.
It contained 45 moles and had a pH of about 5.3. Thereafter, in the same manner as in Example 2, P _1.5 Mo ₁₂ V _1.0 Cs
A catalyst having a composition of _1.8 Cu _0.1 was prepared. The result of the activity test similar to that in Example 1 was that the conversion of methacrolein was 86.4.
% And methacrylic acid selectivity was 81.0%.

Comparative Example 3 During the preparation of the catalyst of Example 3, the molded product was calcined at 360 ° C. in air without calcining in a nitrogen stream to obtain a catalyst. As a result of infrared spectroscopy of this catalyst, it was found that ammonium roots remained. The quantitative analysis result of the sulfur content was 0.6% by weight. As a result of the activity test similar to that in Example 1, the conversion of methacrolein was 76.2% and the selectivity of methacrylic acid was 79.8%. As compared with Example 3,
If firing is not performed under an inert gas atmosphere,
Low selectivity.

Comparative Example 4 Phosphomolybdic acid (H_ThreePMo₁₂O₄₀・ 30H_TwoO) 1
18.2 g and 8.65 g of 85% phosphoric acid were added to ion-exchanged water 5
Vanadium pentoxide (V)_TwoO _Five) 4.
Add 54g, reflux at 100 ° C for 5 hours and homogenize
A solution was obtained. To this, add and dissolve copper nitrate (1.2 g).
17.5 g of cesium nitrate and ammonium sulfate ((NH
_Four)_TwoSO_Four) Dissolve 9.9g in 150ml ion exchange water
The solution was added to form a slurry. In this slurry
Is 3 mol of ammonium radical and 12 mol of sulfate per 12 mol of Mo
It contained 1.5 moles and had a pH of about 2.0.

This slurry was concentrated using a rotary evaporator and dried at 120 ° C. This is X
It was a Keggin-type heteropolyacid salt by X-ray diffraction and infrared spectroscopy. This was calcined at 435 ° C. for 5 hours in a stream of nitrogen, and then graphite was added to form a tablet. 3 in the air
It was calcined at 80 ° C. for 3 hours to obtain a catalyst. Example 3
Is the same as As a result of the activity test similar to that in Example 1, the conversion of methacrolein was 73.8% and the selectivity of methacrylic acid was 7
It was 6.8%. When the pH of the slurry is low, both the activity and the selectivity are low.

Example 4 A life test was performed using the catalyst of Example 2. The reaction conditions were the same as in Example 1, except that the reaction temperature for long-term operation was 300 ° C.
The test was performed at 280 ° C. only during the activity test. as a result,
The reaction results 200 days after the start of the test were methacrolein conversion 92.3% and methacrylic acid selectivity 84.2%.

Comparative Example 5 The same life test as in Example 4 was performed using the catalyst of Comparative Example 3. After 200 days, the conversion of methacrolein was 7
0.6% and methacrylic acid selectivity were 79.2%.

Example 5 Using the catalyst of Example 2, an oxidation reaction of isobutane was performed. 9 g of the catalyst was filled in a glass reaction tube having an inner diameter of 15 mm,
A raw material gas consisting of 42 mol% of isobutane, 33 mol% of oxygen, 12 mol% of water vapor, and the balance of nitrogen was supplied at a space velocity (STP
(Reference) 600 h ^-1 . The reaction pressure was 1.5 atm. When the reaction temperature was set to 300 ° C. and the analysis was performed 15 hours after the start of the reaction, the conversion of isobutane was 10.1%, the selectivity of methacrylic acid was 50.6%, and the selectivity of methacrolein was 13.2%.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiaki Ui 5-1 Sokai-cho, Niihama-shi, Ehime Sumitomo Kagaku Kogyo Co., Ltd. (72) Inventor Tetsuya Yamamoto 5-1 Sokai-cho, Niihama-shi, Ehime (56) References JP-A-4-63139 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-37/36 C07B 61/00 C07C 57/05

Claims (3)

(57) [Claims] 1. The general formula PaMobVcAsdXeYfOg (wherein P, Mo, V, As and O represent phosphorus, molybdenum, vanadium, arsenic and oxygen, respectively, and X is selected from the group consisting of potassium, rubidium, cesium and thallium. Y represents at least one element selected from the group consisting of copper, silver, bismuth, iron, cobalt, antimony, lanthanum and cerium, and subscripts a, b, c, d and e , F and g represent the atomic ratio of each element, and when b = 12, a, c and e are 0
Value of 3 or less not including (zero), d and f are 0 (zero)
And g is a value determined by the valence and atomic ratio of other elements), and is a methacrylic acid comprising a partially neutralized salt of a heteropolyacid substantially free of ammonium and sulfate groups. When producing a production catalyst, the pH of a solution obtained by dissolving or suspending all the catalyst raw materials in water has a pH of 3 to
9. A catalyst for producing methacrylic acid, characterized in that a solid obtained by concentrating and drying the solution is calcined at 400 to 500 ° C. in an inert gas atmosphere in the presence of an ammonium group and a sulfate group so as to fall within the range of 9. Manufacturing method. 2. A solution prepared by dissolving or suspending all catalyst raw materials in water at 80 to 250 ° C. in the presence of saturated steam.
The method for producing a catalyst for producing methacrylic acid according to claim 1, wherein the heat treatment is performed for a time. 3. The amount of ammonium radical and sulfate radical in a solution obtained by dissolving or suspending a catalyst raw material in water is 6 to 18 mol and 0.1 to 3 mol, respectively, based on 12 mol of molybdenum. 2. The method for producing a catalyst for producing methacrylic acid according to 1.